Bag

ABSTRACT

A bag ( 100 ) is disclosed as including an opening at an open end ( 102 ) and a seal ( 108 ) adjacent to a closed end ( 104 ), in which the bag is movable between a collapsed configuration in which the bag is flat and an expanded configuration in which the opening is closed and the bag is fully inflated, and the seal is non-straight when the bag is in the collapsed configuration, and the seal is straight when the bag is in the expanded configuration.

[0001] This invention relates to a bag, e.g. a bag made of a synthetic material, which may be used for containing refuse.

BACKGROUND OF THE INVENTION

[0002]FIGS. 1A to 1C show various views of a conventional bag 10 made of a sheet of plastic material. FIG. 1A shows a view of the plastic bag 10 in a fully collapsed configuration, and

[0003]FIG. 1B shows a sectional view of the plastic bag 10 taken along a line P-P in FIG. 1A. During the production of the plastic bag 10, a width of the sheet of plastic material is folded inward of a respective designed lateral edge of the bags 10, each forming a gusset, and a straight seal 12 is then formed near the intended bottom end and transverse to the length of the bag 10, by heat sealing at a temperature of 200 to 350° C. in the conventional manner. It is however found in practice that the region between two points, namely M and N shown in FIGS. 1A and 1B, where the seal 12 meets the gussets is the weakest in terms of loading capacity. This usually results in leakage of the contents in the bag 10 through or around this region, or the bag 10 is torn apart around the region between the points M and N, on the weight of the contents.

[0004] This phenomenon can be more clearly explained with reference to FIG. 1B. In particular, it is found that when such a conventional plastic bag 10 is fully expanded, i.e. fully inflated and closed at its mouth in an airtight manner, the seal 12 is bent with its mid portion, i.e. the region between the points M and N, nearer to the mouth of the bag 10 than the rest of the seal 12. In this way, the region between the points M and N will have to bear a higher proportion of the pressure exerted by the contents in the bag 10 on the seal 12 than the rest of the seal 12. Put another way, the pressure exerted by contents in the bag 10 on the seal 12 is not even, thus causing some part of the seal, namely the region between the points M and N in the bag 10 shown in FIG. 1B, to bear a higher pressure than other part of the seal 12.

[0005] It is thus an object of the present invention to provide a bag in which the aforesaid shortcomings are mitigated, or at least to provide a useful alternative to the public.

[0006] It is a further object of the present invention to provide a bag with a higher loading capacity, as compared with a conventional bag made of the same type and amount of material.

SUMMARY OF THE INVENTION

[0007] according to the present invention, there is provided a bag with an opening at a first end and at least a seal adjacent to a second end, wherein said bag is movable between a collapsed configuration in which said bag is substantially flat and an expanded configuration in which said bag is fully inflated and said opening is closed, characterized in that said seal is non-straight when said bag is in said collapsed configuration.

BRIEF DESCRIPTION OF THE INVENTION A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0008]FIG. 1A is a side view of a prior art plastic bag in a fully collapsed configuration;

[0009]FIG. 1B is a side view of the plastic bag shown in FIG. 1A, in a fully expanded configuration;

[0010]FIG. 1C is a sectional view of the prior art plastic bag taken along the line P-P in FIG. 1A;

[0011]FIG. 2 is a side view of a plastic bag according to the present invention in a fully collapsed configuration; and

[0012]FIG. 3 is a side view of the plastic bag shown in FIG. 2, in a fully expanded configuration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0013]FIG. 2 shows a side view of a plastic bag according to a preferred embodiment of the present invention, generally designated as 100, in a fully collapsed configuration. The bag 100 has an open end 102, and a closed end 104. The open end 102 may be closed in a substantially airtight manner by strings (not shown) or such other conventional closure means. The bag 100 may be made of such plastic material as low density or high density polyethylene.

[0014] The bag 100 is shown here as formed with two seals, namely a straight seal 106, represented by a straight line ST in FIG. 2, and a non-straight seal 108, represented by a non-straight line AG, both close to the closed end 104. In this connection, although the seal 106 is of the same structure as the seal 12 of the bag 10 shown in FIG. 1A, it is in fact only of cosmetic purpose in the bag 100, for the reasons to be discussed below.

[0015] Referring to FIG. 2, it can be seen that, when the bag 100 is in this fully collapsed configuration, the seal 108 is non-straight. In particular, the seal 108 is made up of a straight line segment AB starting from one lateral edge of the bag 100 leading downwardly towards the closed end 104, joined by an arc BC with a centre of curvature O₂ downward of the seal 108, followed by an arc CDE with a centre of curvature O₁ upward of the seal 108, followed by an arc EF with a centre of curvature O₃ downward of the seal 108, then a straight line segment FG ending at the other lateral edge of the bag 100. It can be seen that the centre of curvature O₁ is on the longitudinal centre line L-L of the bag 100. The arcs BC and EF are thus curved towards the open end 102, and the arc CDE is curved towards the bottom end 104. The line ABCD is symmetrical to the line GFED about the longitudinal centre line L-L. It can also be seen that the line segments AB and FG, when extended when the bag 100 is in the fully collapsed configuration, will intersect an angle e, which is an obtuse angle.

[0016] The width of the bag 100 may be from 300 mm to 1,000 mm, depending on customer requirements, and the width of the seals 106 and 108 may be from 0.8 mm to 2 mm. The ranges of other dimensions are as follows:

[0017] R₁: 100 mm to 300 mm;

[0018] f: 3 mm to 15 mm;

[0019] a: 10 to 100 mm;

[0020] b: 130 mm to 340 mm.

[0021] As to the value of R₂, such can be determined by reference to the value off and b, since the circle of which the arc BC forms a part only touches the circle of which the arc CD forms a part, and the line segment AB, when extended, is tangent to the arc CD.

[0022] It can be seen that the distance between the points A and G to the open end 102 is shorter than the distance between the point D (where the seal 108 intersects the longitudinal centre line L-L of the bag) and the open end 102.

[0023] When the bag 100 according to the present invention is in its fully expanded configuration, i.e. fully inflated and substantially airtightly closed adjacent to the open end 102, although the seal 106 will still be bent upwardly towards the mouth of the bag 100, the seal 108 will however constitute a straight line, as can be seen in FIG. 3. By reason of such a change in the shape of the seal 108, the whole of the seal 108 will contribute equally to bearing the loading of the content in the bag 100, thus increasing the loading capacity of the bag 100, when the bag 100 is in its fully expanded configuration. It is found in experiments that the loading capacity of a bag made in accordance with the present invention can be as much as eight times that of a conventional bag, i.e. one with the conventional seal 12 only, made of the same type and amount of material.

[0024] As the weight of the contents in the bag 100 will be borne by the seal 108 only, the seal 106 is only of cosmetic purpose only, i.e. to enhance the aesthetic appearance of the bag 100, but does not contribute to the load-bearing capacity of the bag 100. The seal 108 may or may not touch the seal 106, and if the seal 108 is designed not to touch the seal 106, their distance is at the discretion of the manufacturer.

[0025] It should be understood that the above only illustrates and describes an example whereby the present invention may be carried out, and that modifications and/or alterations may be made thereto without departing from the spirit of the invention.

[0026] It should also be understood that various features of the invention which are, for brevity, described in the context of a single embodiment, may be provided separately or in any suitable sub-combination. 

What is claimed is:
 1. A bag (100) with an opening at a first end (102) and at least a seal (108) adjacent to a second end (104), wherein said bag is movable between a collapsed configuration in which said bag is substantially flat and an expanded configuration in which said bag is fully inflated and said opening is closed, characterized in that said seal is non-straight when said bag is in said collapsed configuration.
 2. A bag according to claim 1 further characterized in that said seal is substantially straight when said bag is in said expanded configuration.
 3. A bag according to claim 1 further characterized in that said seal has two end portions joined by a middle portion which intersects a longitudinal centre line (L-L) of said bag, wherein the distance between at least one said end portion and said first end is shorter than the distance between said first end and a point (D) where said middle portion intersects said longitudinal centre line.
 4. A bag according to claim 1 further characterized in that said seal includes at least two straight lines (AB, FG) which, when extended when said bag is in said collapsed configuration, intersect at an angle.
 5. A bag according to claim 1 further characterized in that when said bag is in said collapsed configuration, said seal includes at least a curved portion (BC, CE, EF).
 6. A bag according to claim 5 further characterized in that when said bag is in said collapsed configuration, said seal includes at least two curved portions, at least one curving towards the first end and at least one curving towards the second end.
 7. A bag according to claim 1 further characterized in that said seal is substantially symmetrical about a central longitudinal axis (L-L) of said bag.
 8. A bag according to claim 1 further characterized in including at least a further seal (106) which, when said bag is in said collapsed configuration, is in the form of a straight line.
 9. A bag according to claim 8 further characterized in that said seal (108) is in contact with said further seal (106).
 10. A bag according to claim 8 further characterized in that said seal (108) is out of contact with said further seal (106). 